One of the key problems in microfabrication and especially nanofabrication applied to biology is materials selection. Proper materials must have mechanical stability and the ability to hermetically bond to other surfaces, yet not bind biological molecules. They must also be wettable by water and have good optical properties. In this article, we review some of the attempts to find materials for micro- and nanofluidic systems in biological applications that satisfy these rather conflicting constraints.We discuss the materials properties that make poly (dimethylsiloxane) or non-elastomeric materials more or less suitable for particular applications in biology. We also explore the effects and the importance of surface treatments for integrating biological objects into microfabricated and nanofabricated fluidic devices.